The present invention generally relates to ultrasonic ranging and, more particularly, to an ultrasonic ranging system and method for enhancing the utilization of an ultrasonic transducer, especially for use in the passenger compartment of a vehicle.
Ultrasonic sensing techniques have become widely acceptable for use in ranging systems for determining the presence of and distance to a target object. In a conventional ultrasonic ranging system, an ultrasonic transducer is employed which converts electrical signal pulses into mechanical motion. In turn, the mechanical motion creates ultrasonic sound waves that are transmitted through the atmosphere in a desired direction. Provided there is a target in its path, the sound waves reflect off the target and the reflected sound waves travel back to the ultrasonic transducer. The reflected sound waves, also referred to as the echo waves, mechanically deflect the ultrasonic transducer and, in response, a low voltage pulsed signal is generated. Since the speed of travel of the sound waves remains relatively fixed, the distance to the target is determined by measuring the time period between the transmitted and received signal pulses, and computing the distance as a function of the time period and the sound wave speed.
The transmitted and received ultrasonic sound waves are similar to audible sound waves, except the ultrasonic frequencies are generally much higher and therefore exceed the audible frequency range for human beings. Accordingly, human beings are generally unable to hear the radiated ultrasonic sound waves generated by the ultrasonic transducer. In many conventional applications, the ultrasonic ranging system is generally considered to be a quiet operating device. However, in practice it is recognized that an ultrasonic transducer creates undesired audible waves as a side effect when transmitting ultrasonic sound waves, particularly at certain strength levels. The presence of audible sound is even more noticeable where a high strength signal is required. It has been discovered that these undesirable audible sound waves generally provide a noticeable audible "tick" sounding noise which, in the past, has generally been considered acceptable for some applications. However, the audible "tick" noise generated by an ultrasonic transducer can be annoying when used in certain environments, such as inside the passenger compartment of a vehicle.
Accordingly, it is one object of the present invention to provide for a method of effectively reducing or eliminating the audible sound noise that may otherwise be produced by an ultrasonic transducer. It is another object of the present invention to provide for an ultrasonic transducer ranging system with reduced or eliminated audible sound noise. Yet, it is a further object of the present invention to provide for quiet and effective use of an ultrasonic transducer in a passenger compartment of a vehicle.